Authentication limit extensive header size

Question

I have an Asp .net mvc app that connects to an Identity server 4 identity server. When i released the app I was fased with this error.

upstream sent too big header while reading response header from upstream

Which i have tracked to this upstream sent too big header while reading response header from upstream

I can not alter the config and sys admin has stated that we need to make the headers smaller.

After looking at that i would have to agree that these headers are a bit extensive.

Startup.cs in app

services.AddAuthentication(options =>
        {
            options.DefaultScheme = CookieAuthenticationDefaults.AuthenticationScheme;
            options.DefaultChallengeScheme = OpenIdConnectDefaults.AuthenticationScheme;
        })
        .AddCookie(CookieAuthenticationDefaults.AuthenticationScheme)
        .AddOpenIdConnect(OpenIdConnectDefaults.AuthenticationScheme, options =>
            {

                options.SignInScheme = CookieAuthenticationDefaults.AuthenticationScheme;
                options.Authority = Configuration["ServiceSettings:IdentityServerEndpoint"];
                options.RequireHttpsMetadata = true;
                options.ClientId = Configuration["ServiceSettings:ClientId"];
                options.ClientSecret = Configuration["ServiceSettings:secret"];
                options.Scope.Add("testapi");
                options.ResponseType = "code id_token";
                options.SaveTokens = true;
                options.GetClaimsFromUserInfoEndpoint = true;
                options.Events = new OpenIdConnectEvents()
                {
                    OnRemoteFailure = ctx =>
                    {
                        _logger.LogCritical($"Remote Faliure: {ctx.Failure}");
                        ctx.HandleResponse();
                        return Task.FromResult(0);
                    }
                };
            });

I have been looking all over and i cant seem to find a way of limiting the size of this huge header.

Answer 1

By default, cookie contains all relevant information, encrypted, so when call to your api is made - all you need to do is decrypt cookie and use that information.

However, often storing everything in a cookie itself is not desirable, especially if there is a lot of relevant information. Cookie is sent with every request to your api, and if it's big - a lot of (the same) information is sent back and forth basically for nothing. Plus as you see yourself - size of cookie might become a limiting factor in some environments.

So instead of sending all information in cookie itself - you can store that information somewhere else, for example in server memory, and place only identifier for that information in cookie itself.

You can configure store for session like this:

services.AddAuthentication(options =>
{
    options.DefaultAuthenticateScheme = CookieAuthenticationDefaults.AuthenticationScheme;
    options.DefaultChallengeScheme = CookieAuthenticationDefaults.AuthenticationScheme;
}).AddCookie(o => o.SessionStore = new MemoryCacheTicketStore());

And you can find sample MemoryCacheTicketStore implementation at asp.net examples on github:

public class MemoryCacheTicketStore : ITicketStore
{
    private const string KeyPrefix = "AuthSessionStore-";
    private IMemoryCache _cache;

    public MemoryCacheTicketStore()
    {
        _cache = new MemoryCache(new MemoryCacheOptions());
    }

    public async Task<string> StoreAsync(AuthenticationTicket ticket)
    {
        var guid = Guid.NewGuid();
        var key = KeyPrefix + guid.ToString();
        await RenewAsync(key, ticket);
        return key;
    }

    public Task RenewAsync(string key, AuthenticationTicket ticket)
    {
        var options = new MemoryCacheEntryOptions();
        var expiresUtc = ticket.Properties.ExpiresUtc;
        if (expiresUtc.HasValue)
        {
            options.SetAbsoluteExpiration(expiresUtc.Value);
        }
        options.SetSlidingExpiration(TimeSpan.FromHours(1)); // TODO: configurable.

        _cache.Set(key, ticket, options);

        return Task.FromResult(0);
    }

    public Task<AuthenticationTicket> RetrieveAsync(string key)
    {
        AuthenticationTicket ticket;
        _cache.TryGetValue(key, out ticket);
        return Task.FromResult(ticket);
    }

    public Task RemoveAsync(string key)
    {
        _cache.Remove(key);
        return Task.FromResult(0);
    }
}